The invention relates to an injection valve. It is known to supply internal combustion engines with fuel using fuel injection systems that operate with a very high injection pressure. Such injection systems are commonly referred to known as common rail systems (for Diesel engines) and PDI injection systems (for Otto cycle engines). In conventional injection systems, fuel is pumped with a high-pressure pump into a pressure reservoir common to all cylinders of the engine. Injection valves supply fuel from the reservoir to individual cylinders. The opening and closing of the injection valves, also known as injectors, is conventionally performed electrically or electromagnetically.
The injection valves in conventional systems are generally provided with servo valves that hydraulically operate the opening and closing of the needle of the actual injection valve, i.e., the servo valves determine the beginning and the end of the injection period. The servo valve, in connection with other features of these systems, mainly influences the speed at which the injection valve opens and closes.
For reasons relating to combustion technology, the speed that the injection valve opens is chosen to be different from the speed that the injection valve closes. The injection valve must, in common rail systems for Diesel engines, open slowly under control at the start of the injection period for better mixing of the fuel with the air. On the other hand, the injection valve must close rapidly at the end of the injection so as to prevent carbon deposit formation. Also, the period of the injection must be controllable. In order to optimize the combustion process, it is desirable to minimize pilot injection, i.e., the amount of fuel that is injected before the actual injection.
Uncontrolled opening of the injection valve can lead to violent pressure fluctuations, which are difficult to overcome, in the high-pressure range of the injection nozzle. By appropriate measures such as control throttling in the fuel delivery, the injection can be controlled at the beginning. Control throttling also has the advantage that the requirements regarding valve timing are substantially less stringent.
A disadvantage of these conventional systems and their known manner of operation is that fuel delivery is not controlled only in the initial phase of the injection, but also when a transition is made from the initial phase to the main phase of the injection, which is to take place as rapidly as possible.